1. Field of the Invention
The present invention relates to a hardness measurement reagent used for measuring a hardness of industrial water, daily life water, and the like.
2. Description of the Related Art
As is well known, a device for removing hardness components (Ca2+ and Mg2+) in raw water such as industrial water or daily life water is connected to a feed water line to cooling/heating equipment such as a boiler, a water heater, and a cooler from a need of prevention of scale deposition within the cooling/heating equipment. For example, a water softening device employing an ion-exchange resin is connected to a feed water line, to thereby replace the hardness components (Ca2+ and Mg2+) in raw water by Na+ and supply the obtained softened water as feed water to the cooling/heating equipment.
In the case where the water softening device is used, degradation of the ion-exchange resin held inside the device or insufficient regeneration of the ion-exchange resin causes insufficient replacement of the hardness components in feed water by Na+. Thus, an allowable hardness must be set in advance according to a hardness or the like of raw water in a region or place where the cooling/heating equipment is provided, and a hardness of the feed water passed through the water softening device must be measured periodically. A hardness of the feed water exceeding the upper limit (hereinafter, referred to as “control hardness”) of an allowable value indicates hardness leakage. Thus, the ion-exchange resin is changed, regenerated, or the like to adjust the feed water within a predetermined hardness range.
There is disclosed a method of measuring a hardness of feed water involving, for example: adding a nonaqueous hardness measurement reagent containing as a dye Eriochrome Black T (EBT) to sample water sampled from feed water; and using a hue of the sample water as an index of a hardness (see JP 11-064323 A, JP 2002-181802 A, and JP 2002-181803 A). The hue of the sample water is qualitatively determined from an abundance ratio of a chelate compound formed through a reaction between hardness components and a dye in the hardness measurement reagent, to an unreacted (free) dye. To be specific, when EBT is used as a dye, a hue of sample water changes from an initial blue color to a bluish purple color (hereinafter, a hardness displaying a hue of a bluish purple color is referred to as a “color change starting point”), to a reddish purple color, and then to a red color (hereinafter, a hardness displaying a hue of a red color is referred to as a “color change end point”) with increasing hardness of the sample water.
A control hardness is set in advance when the hardness leakage is detected by focusing on such a change in hue corresponding to a hardness of the sample water. Further, measuring conditions such as a mixing ratio of EBT in a hardness measurement reagent, an amount of the hardness measurement reagent added during measuring, and a volume of the sample water are determined such that the control hardness falls within a range between the color change starting point and the color change end point. Then, an actual measuring operation is conducted.
Thus, when the change in hue corresponding to a hardness of the sample water is used as an index of hardness leakage, a hue measuring method generally employs visual measuring through observation by humans or mechanical measuring through transmittance measurement or absorbance measurement. In the visual measuring, a change in hue of the sample water to a bluish purple color or to a red color indicates the hardness leakage. Further, in the mechanical measuring, a hardness is directly displayed on a measuring device based on a calibration curve showing a relationship between a hardness and a transmittance (or absorbance), and a hardness reaching the control hardness indicates the hardness leakage. In either measuring method, coloring of a dye is desirably not interfered with interfering substances in the sample water in order to display a hue corresponding to a hardness for reliable detection of the hardness leakage.
However, studies of the inventors of the present invention have confirmed that coloring of the sample water using a conventional hardness measurement reagent tends to be more interfered with a higher M alkalinity of the feed water. This tendency does not particularly cause problems in the visual measuring because the M alkalinity has a small effect on the hue of the sample water. However, the tendency results in a difference between an actual hardness and a measured hardness in the mechanical measuring, and thus improvements of the hardness measurement reagent have been desired for reliable detection of the hardness leakage of water having a high M alkalinity.